Implantable electrode and method of making the same

ABSTRACT

An implantable electrode system of is disclosed that includes a conductive electrode layer, an interconnect coupled to the electrode layer, an insulator that insulates the interconnect, and an anchor that more securely fixes the electrode layer in place. This structure is particularly useful with the electrode layer being a neural interface that is configured to provide either a recording or stimulating function. A method for forming such an implantable electrode system includes forming an interconnect over a base layer, forming an anchoring structure over the base layer, depositing an insulating material layer over the interconnect structure and over the anchoring structure, exposing a portion of the interconnect structure, forming an electrode layer over the insulating layer, the electrode layer contacting the exposed portion of the interconnect structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/676,037, filed on Apr. 1, 2015, now U.S. Pat. No. 9,656,054, which isa divisional of U.S. patent application Ser. No. 13/713,115, filed onDec. 13, 2012, now U.S. Pat. No. 9,265,928, which is a divisional ofU.S. patent application Ser. No. 12/396,107, filed on Mar. 2, 2009, nowU.S. Pat. No. 8,498,720, which claims the benefit of U.S. ProvisionalApplication Ser. No. 61/032,725, filed on Feb. 29, 2008, all of whichare incorporated herein in their entirety by this reference.

TECHNICAL FIELD

This invention relates generally to the implantable electrodes field,and more specifically to an improved implantable electrode with ananchoring element and the method of making this improved system.

BACKGROUND

The adhesion of metals to polymers in conventional microfabricationtechniques can be quite poor. Excellent adhesion, however, is criticalfor biomedical electrodes, which are implanted in tissue and are exposedto harsh environments. In such environments, poorly connected elementscan lead to irreversible chemical reactions and possible device failure.The irreversible chemical reactions can include: 1) electrolysis ofwater, with consequent pH changes and gas formation, 2) electrodedissolution due to oxide formation of soluble metal complexes, and 3)corrosion or breakdown of passivity. In conventional electrodes, unevencharging across the electrode site is often seen. As an example, a muchhigher current density is typically seen in the perimeter of theelectrode site than seen in the center, thus when the electrode isplaced onto the tissue of the patient, the uneven charging may lead tounpredictable stimulation of the tissue of the patient. Uneven chargingacross the electrode site also leads to additional irreversible chemicalreactions. In the case of higher current density along the perimeterthan seen in the center, a relatively high potential difference betweenthe perimeter of the electrode and the center of the electrode develops,leading to a higher chance of irreversible chemical reactions at theedge of the electrode site. This invention provides an improved anduseful system and method for connecting layers within an electrode,increasing the reliability of an electrode, and decreasing the chance ofirreversible chemical reactions within an electrode.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view of the implantable electrode of thepreferred embodiment including a first variation of the anchoringelement.

FIG. 2 is a cross-sectional view of the implantable electrode of thepreferred embodiment including a second variation of the anchoringelement.

FIG. 3 is a cross-sectional view of the implantable electrode of thepreferred embodiment including a third variation of the anchoringelement.

FIG. 4 is a top view and cross-sectional view of an implantableelectrode.

FIG. 4A is a cross-sectional view along line 4A-4A of FIG. 4.

FIG. 5A is a graphical representation of the effect on current densityacross the electrode site of the preferred embodiment with the thirdvariation of the anchoring element.

FIG. 5B is a graphical representation of the double layer final voltageacross the electrode site of the preferred embodiment with the thirdvariation of the anchoring element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of preferred embodiments of the invention isnot intended to limit the invention to these embodiments, but rather toenable any person skilled in the art to make and use this invention.

As shown in FIG. 1, the implantable electrode 10 of the preferredembodiments includes an electrode site 12, an interconnect 14 coupled tothe electrode site 12, an insulating element 16 that functions toinsulate the interconnect 14, and an anchoring element 18 that functionsto anchor the electrode site 12 to the implantable electrode 10. Theimplantable electrode 10 of the preferred embodiment is preferablydesigned for an implantable electrode lead system to interface withbrain tissue, the implantable electrode 10 of the preferred embodiments,however, may be alternatively used in any suitable environment (such asthe spinal cord, peripheral nerve, muscle, or any other suitableanatomical location) and for any suitable reason.

1. The Implantable Electrode

As shown in FIGS. 1, 4 and 4A, the electrode site 12 of the preferredembodiment functions to record, stimulate, perform any other suitablefunction, or any combination thereof. The implantable electrodepreferably includes a plurality of electrode sites 12, which may beindependently tuned to record, stimulate, perform any other suitablefunction, or any combination thereof. Two or more electrode sites 12 maybe grouped to form a larger composite site that enables tuning theneural interface region for recording and/or stimulation. The electrodesite 12 is preferably a thin film metal, preferably made from gold,iridium, or platinum, but may alternatively be made from any suitablematerial.

The implantable electrode 10 of the preferred embodiments may furtherinclude a bond pad, which is electrically coupled to the electrode site12 and functions to provide a point of contact to an external connectorand/or device to provide a site from which recorded signals are accessedand/or to which stimuli are applied. The implantable electrodepreferably includes a plurality of bond pads. The ratio of electrodesites 12 to bond pads is preferably 1:1, but may be any other suitableratio. The bond pads are preferably gold, but may alternatively be anysuitable material.

The implantable electrode 10 of the preferred embodiments may furtherinclude a plug 20 (also known as “leg”), which couples the electrodesite 12 to the interconnect 14 and functions to transfer signals betweenthe electrode site 12 and the interconnect 14. The implantable electrodepreferably includes a plurality of plugs 20. The ratio of electrodesites 12 to plugs 20 is preferably 1:1, but may be any other suitableratio. The plug 20 is preferably gold or platinum, but may alternativelybe any suitable material.

As shown in FIGS. 1, 4 and 4A, the interconnect 14 of the preferredembodiment is coupled to the electrode site and functions toelectrically couple the electrode site 12 to a bond pad or directly toan external connector and/or device and to transfer signals between theelectrode site 12 and the bond pads, connector, and/or device. Theimplantable electrode preferably includes a plurality of interconnects14. The ratio of electrode sites 12 to interconnects 14 is preferably1:1, but may be any other suitable ratio. The interconnect 14 ispreferably metal (such as platinum or gold) or polysilicon, but mayalternatively be made out of any suitable material.

As shown in FIGS. 1, 4 and 4A, the insulating element 16 of thepreferred embodiment functions to insulate the interconnect 14,preferably on the top and bottom side of the interconnect 14. Theinsulating element 16 is preferably one of several variations, and insome variations the insulating element 16 preferably includes multiplelayers: a first layer 16 and a second layer 16′. In a first variation,where the interconnect 14 is preferably a metal such as platinum orgold, the insulating element 16 is preferably a polymer such aspolyimide, parylene, or polydimethylsiloxane (PDMS). In a secondvariation, where the interconnect 14 is preferably polysilicon, theinsulating element preferably includes a first layer 16 of inorganicdielectrics such as silicon dioxide or silicon nitride and a secondlayer 16′ of a polymer. In a third variation, where the interconnect 14is preferably polysilicon, the insulating element preferably includes afirst layer 16 of inorganic dielectrics such as silicon dioxide orsilicon nitride that are supported by a silicon substrate. The firstlayer 16 of inorganic dielectrics are preferably a tri-layer stack ofsilicon dioxide, silicon nitride, and silicon dioxide. Alternatives tothe first layer 16 include silicon carbide and other polymers such aspolyimide or parylene. The second layer 16′ may be the same as the firstlayer, or may alternatively be a vapor deposited polymer such asparylene, Polytetrafluoroethylene (PTFE), other fluoropolymers,silicone, or any other suitable material. The second layer 16′preferably provides additional electrical insulation to leads.

As shown in FIGS. 1-3, the anchoring element 18 of the preferredembodiment functions to anchor the electrode site 12 to the implantableelectrode 10. The anchoring element is preferably one of severalvariations, in a first variation, as shown in FIG. 1, the anchoringelement 18 is a layer of metal. This metal layer is preferably locatedabove the interconnect 14 such that it will not short or interfere withthe interconnect 14. The metal layer is preferably located on the topsurface of the second layer 16′ of the insulation element 16. The metalelectrode site 12 will adhere to the metal anchoring element 18, Thestrong metal-to-metal adhesion of the electrode site 12 to the anchoringelement 18 preferably complements the adhesion of the electrode site 12to the implantable electrode 10 (i.e. the top polymer surface). Theanchoring element 18 in this variation is preferably buried in and/orunder an additional layer 16″ (preferably a polymer) of the insulationelement 16 with a portion of the anchoring element 18 exposed to contactthe electrode site 12. The exposed portion of the anchoring element 18of this variation is preferably patterned to have a ring geometry thatcoincides with a perimeter portion of the electrode site 12.Alternatively, the exposed portion of the anchoring element 18 may forma semi-ring, may have multiple points, or may have any other suitablegeometry. The geometry of the exposed portion of the anchoring element18 may be defined by the anchoring element 18 and/or the additionallayer 16″ of the insulation element 16 and the pattern in which theanchoring element 18 is exposed.

In a second variation, as shown in FIG. 2, the anchoring element 18 isalso a layer of metal, but this layer of metal is preferably located atthe level of the interconnects 14 and is preferably insulated by theinsulation element layers 16 and 16′. The metal electrode site 12 willadhere to the metal anchoring element 18. The strong metal-to-metaladhesion of the electrode site 12 to the anchoring element 18 preferablycomplements the adhesion of the electrode site 12 to the implantableelectrode 10 (i.e. the top polymer surface). The anchoring element 18 ofthis variation preferably does not require the additional layer 16″ ofthe insulation element 16, but rather, is preferably buried in thesecond layer 16′ with a portion of the anchoring element 18 exposed tocontact the electrode site 12. The anchoring element 18 of thisvariation is preferably patterned to have multiple points or “spots”that coincide with the perimeter portion of the electrode site 12, andare preferably positioned such that the multiple points will not crossover or connect adjacent interconnects 14. Alternatively, the exposedportion of the anchoring element 18 may form a semi-ring or may have anyother suitable geometry. The anchoring element 18 of this variation mayfurther include a plug 22, which couples the electrode site 12 to theanchoring element 18. The plug 22 is preferably gold or platinum, butmay alternatively be any suitable material.

In a third variation, as shown in FIG. 3, the anchoring element 18 is alayer of an insulating material, such as a polymer, that functions tomechanically couple the electrode site 12 to the implantable electrode10. The mechanical coupling of the electrode site 12 to the anchoringelement 18 preferably complements the adhesion of the electrode site 12to the implantable electrode 10 (i.e. the top polymer surface). Theanchoring element 18 is preferably an additional layer of the insulationelement 16. The anchoring element 18 is preferably located on the topsurface of the second layer 16′ of the insulation element 16. Theelectrode site 12 in this variation is preferably buried in and/or underthe anchoring element 18 with a portion of the electrode site exposed.The exposed portion will record, stimulate, perform any other suitablefunction, or any combination thereof. The anchoring element 18 ispreferably patterned to form a lip or a rim around the perimeter portionof the electrode site 12. Alternatively, the anchoring element 18 mayhave any other suitable geometry.

As shown in FIGS. 5A and 5B, the third variation of the anchoringelement 18 also functions to normalize (or “make more uniform”) theinitial current distribution along the electrode site 12. Inconventional implantable electrodes, as a stimulation pulse is sent tothe electrode site 12, the initial current density along the electrodesite 12 is not uniform. The current density along the perimeter of theelectrode site 12 is higher than that at the center of the electrodesite 12, leading to uneven changing across the electrode site 12 andcreating a potential difference between the perimeter and the center ofthe electrode site 12. The difference in potential may lead tounpredictable stimulation of the tissue of the patient, such as chargespikes along the electrode site 12, and an increased chance ofirreversible chemical reactions at the perimeter of the electrode site12, thereby potentially releasing toxic products into the tissue of thepatient and decreasing the effectiveness of the electrode 10. The thirdvariation of the anchoring element 18 provides a raised lip along theperimeter of the electrode site 12. This raised lip has been shown todecrease the difference in initial current densities along the electrodesite 12, as shown in FIG. 5A, leading to a more normalized final voltagepotential distribution along the electrode site 12, as shown in FIG. 5B,increasing the reliability of the electrode and decreasing the chance ofirreversible chemical reactions.

The anchoring element 18 of the third variation may alternatively beshaped to accommodate to the type of charge distribution desired acrossthe electrode site 12. For example, a higher charge distribution may bedesired in a first region than in a second region of the electrode site12. To achieve this, the raised lip may be thicker in the second regionthan in the first region. Alternatively, the raised lip of the anchoringelement 18 may be of a uniform thickness around the perimeter of theelectrode site 12 to achieve higher mitigation of the current density atthe perimeter. However, any other arrangement of the anchoring element18 suitable to regulate the charge distribution across the electrodesite 12 may be used.

The anchoring element 18 of the third variation may also be shaped toaccommodate to the type of mechanical interlock desired across theelectrode site 12. For example, the raised lip of the anchoring element18 may be shaped as an “X” across the electrode site 12, but mayalternatively also be shaped as parallel ridges across the electrodesite 12. However, any other arrangement of the anchoring element 18suitable to provide an adequate mechanical interlock across theelectrode site 12 may be used.

2. Method of Making the Implantable Electrode

The implantable electrode 10 of the preferred embodiment is preferablymicro-machined using standard microfabrication techniques, but mayalternatively be fabricated in any other suitable fashion. As shown inFIGS. 4 and 4A, the method of building an implantable electrode of thepreferred embodiments includes building a first layer of the insulatingelement 16 S102, building an interconnect 14 S104, building a secondlayer 16′ of the insulating element S106, removing a portion of thesecond layer 16′ to expose a portion of the interconnect 14 S108,building a layer of conductive material to fill the second layer 16′S110, and building the electrode site 12 S112.

The method of building an implantable electrode with an anchoringelement 18 of the preferred embodiments preferably includes additionaland/or alternative steps to build the anchoring element 18 in one ofseveral variations. In a first variation, as shown in FIG. 1, after StepS106 the method of the first variation includes building an anchoringelement 18 S114, building a third layer 16″ of the insulating element 16S116, removing a portion of the third layer 16″ to expose a portion ofthe anchoring element 18 and to expose a portion of the second layer 16′above the interconnect 14 S118, removing a portion of the second layer16′ to expose a portion of the interconnect 14 S108, building a layer ofconductive material to fill the second layer 16′ and the portion of thethird layer 16″ above the interconnect 14 S110′, and building theelectrode site 12 S112.

In a second variation, as shown in FIG. 2, the method of the secondvariation includes an alternative Step S104′: building an interconnect14 and an anchoring element 18, and an alternative Step S108′: removinga portion of the second layer 16′ to expose a portion of theinterconnect 14 and the anchoring element 18. In a third variation, asshown in FIG. 3, the method of the third variation includes twoadditional steps after Step S112. Those steps include building ananchoring element 18 S120, and removing a portion of the anchoringelement 18 to expose a portion of the electrode site 12 S122. The methodis preferably designed for the manufacture of implantable electrodes,and more specifically for the manufacture of implantable electrodes withanchoring elements. The method and any variation thereof, however, maybe alternatively used in any suitable environment and for any suitablereason.

Step S102, which recites building a first layer of the insulatingelement 16, functions to provide the base layer of the implantableelectrode 10. The adding of material is preferably performed through anysuitable deposition process that grows, coats, or transfers a materialin any other suitable method.

These deposition processes may include spinning and curing, physicalvapor deposition (PVD), chemical vapor deposition (CVD), electrochemicaldeposition (ECD), molecular beam epitaxy (MBE) and more recently, atomiclayer deposition (ALM, or any other suitable process.

Step S104 and S104′, which recite building an interconnect 14 andbuilding an interconnect 14 and an anchoring element 18 respectively,function to create the interconnects and/or the metal anchoring elements18. This step is preferably performed by building a layer of materialand then patterning the layer of material to form the interconnects 14and/or the anchoring elements 18. The adding of material is preferablyperformed through any suitable deposition process that grows, coats, ortransfers a material in any other suitable method. These depositionprocesses may include sputtering, evaporating, physical vapor deposition(PVD), chemical vapor deposition (CVD), electrochemical deposition(ECD), molecular beam epitaxy, (MBE) and more recently, atomic layerdeposition (ALD), or any other suitable process. The removal orpatterning of material is preferably performed through reactive ionetching (RIE), but may alternatively be performed through any othersuitable removal process, such as other dry etching methods, wetetching, chemical-mechanical planarization, or any combination thereof.

The interconnects 14 and/or the anchoring elements 18 may alternativelybe created by any suitable combination of deposition, removal, and orpatterning.

Step S106, which recites building a second layer 16′ of the insulatingelement is preferably performed in a similar fashion to Step S102 above.

Step S108, S108′, and S118, which recite removing a portion of theinsulating element to expose a portion of the interconnect 14, theanchoring element 18, and/or a lower layer of the insulating elementfunction to expose a contact through the insulating element to the layerbelow. The removal or patterning of material is preferably performedthrough reactive ion etching (RIE), but may alternatively be performedthrough any other suitable removal process, such as other dry etchingmethods, wet etching, chemical-mechanical planarization, or anycombination thereof. The interconnects 14 and/or the anchoring elements18 may alternatively be created by any suitable combination ofdeposition, removal, and or patterning.

Step S110 and S110′, which recite building a layer of conductivematerial to fill a layer of the insulating element, function to build a“plug” (also known as “leg”) to fill the contact hole with conductivematerial and to form the plugs 20 and/or 22. The step is preferablyperformed through electroplating, but may alternatively be performedthrough any suitable deposition process that grows, coats, or transfersa material in any other suitable method.

Step S112, which recites building the electrode site 12, functions tocreate electrode site 12. This step is preferably performed by buildinga layer of material and then patterning the layer of material to formthe electrode site 12. This step preferably uses a method to addmaterial and then remove material as described in Step S104.

Step S114, which recites building an anchoring element 18, functions tocreate the metal layer anchoring element 18 of the first variation. Thisstep is preferably performed by building a layer of material and thenpatterning the layer of material to form the anchoring element 18. Thisstep preferably uses a method to add material and then remove materialas described in Step S104.

Step S116 and Step S120, which recite building an anchoring element 18and building a third layer 16″ of the insulating element 16, function tocreate the anchoring element 18 of the third variation (which ispreferably an insulating material) and to build the third layer of theinsulating element, respectively. This is preferably performed in asimilar fashion as described in Step S102.

Step S122, which recites removing a portion of the anchoring element 18to expose a portion of the electrode site 12, functions to expose acontact through the anchoring element 18 to the electrode site 12. Theremoval or patterning of material is preferably performed through a deepreactive ion etching (DRIE), but may alternatively be performed throughany other suitable removal process, such as other dry etching methods,wet etching, chemical-mechanical planarization, or any combinationthereof.

The interconnects 14 and/or the anchoring elements 18 may alternativelybe created by any suitable combination of deposition, removal, and orpatterning.

Although omitted for conciseness, the preferred embodiments includeevery combination and permutation of the various implantable electrodes,the various interconnects, the various insulation elements, the variousanchoring elements, and the various methods of making the variousimplantable electrodes.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claim, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaim.

What is claimed is:
 1. A method for controlling charge distribution ofan implantable electrode comprising: forming an interconnect structureover a base layer; forming an anchoring structure over the base layer;depositing an insulating material layer over the interconnect structureand over the anchoring structure; exposing a portion of the interconnectstructure through the insulating material layer; exposing a portion ofthe anchoring structure through the insulating material layer; forming afirst plug over the exposed portion of the interconnect structure;forming a second plug over the exposed portion of the anchoringstructure; and forming an electrode site that extends over theinsulating material layer, the first plug, and the second plug, theelectrode site being electrically coupled to the exposed portion of theinterconnect structure via the first plug and to the exposed portion ofthe anchoring structure via the second plug.
 2. The method of claim 1,wherein the electrode site is a thin film of metal comprised of gold,iridium, or platinum.
 3. The method of claim 1, wherein the exposedportion of the interconnect structure has a ring geometry.
 4. The methodof claim 1, wherein exposing the portion of the interconnect structurecomprises: exposing a central portion of the interconnect structurewithout exposing an edge portion of the interconnect structure.
 5. Themethod of claim 1, wherein an edge portion of the interconnect structureis separated from the electrode site by a portion of the insulatinglayer.
 6. The method of claim 1, wherein forming the electrode sitecomprises: forming a metal-to-metal bond between a material of theelectrode site and a material of the second plug.
 7. The method of claim1, wherein the anchoring structure and the interconnect structure areformed on a common plane.
 8. The method of claim 7, wherein theelectrode site is circular and the exposed portion of the anchoringstructure has a ring geometry that coincides with a perimeter portion ofthe electrode site.
 9. The method of claim 1, wherein depositing theinsulating material layer comprises: depositing a first insulatingmaterial layer over and in contact with the interconnect structure; anddepositing a second insulating material layer over and in contact withthe first insulating material layer.